Hallo,
vielleicht hilft Dir dieses Dokument ?

How Much Data and How Much Free Space Is Available on a Tape
Technote

This document explains how to calculate the amount of data that is on a tape cartridge and how much free space is available.

Run the DSPTAP *LABELS command to *PRINT.

To determine how much save/restore data is on a cartridge, add all the file lengths and multiple by (block length less 4096). This gives you how many bytes are written to the tape.

Example

Record
File Block Recg Record Block File Mvol Mvol Date Expiration
Data File Label Sequence Format Tech Length Length Length Ind Sequence Created Date
SAV20070304 0000000001 *U P 00000 262144 0000232033 CONT 0000000001 03/04/07 *PERM

232033 x (262144 - 4096) = 59,875,651,584 B

Data compression, if used, affects this figure; however, there is no way to calculate the effects.

In addition, if using a tape drive that is capable of optimum blocking and Use Optimum Block *YES is specified, there is no way to calculate how much more data can be written to the tape cartridge.

Note: There is a minimum 20 percent margin of error when using this calculation.

If the tape has sequences with different block lengths on it, group the different entries together. Do the calculations for each group, and add them all together to get the total amount of data on the cartridge. 262144 0000232033